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M. Schmitt, U. Wieland, A. Kreuter, and M. Pawlita, scientificreports/ Andermarcher for assistance with her comments and proof-reading that greatly improved the manuscript. The authors received support from 'La Ligue Contre le Cancer' in the form of a PhD studentship (Magali Boyer). Author contributions C.A.-P. and L.C. conceived the concepts of the research. O.D. included the MCC patients, Int. J. Cancer, vol.131, p.1612, 2012.